Danne, and others, have studied the
properties of these emanations.
The substance emanated can neither be weighed nor can its elastic
force be ascertained; but its transformations may be followed, as it
is luminous, and it is even more certainly characterised by its
essential property, i.e. its radioactivity. We also see that it can be
decanted like a gas, that it will divide itself between two tubes of
different capacity in obedience to the law of Mariotte, and will
condense in a refrigerated tube in accordance with the principle of
Watt, while it even complies with the law of Gay-Lussac.
The activity of the emanation vanishes quickly, and at the end of four
days it has diminished by one-half. If a salt of radium is heated, the
emanation becomes more abundant, and the residue, which, however, does
not sensibly diminish in weight, will have lost all its radioactivity,
and will only recover it by degrees. Professor Rutherford,
notwithstanding many different attempts, has been unable to make this
emanation enter into any chemical reaction.
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